This invention relates to optoelectronic couplers and, it relates, more particularly to an optocoupler utilizing a stacked device arrangement wherein the middle layer serves as both the coupling medium and a mechanical bonding medium.
Optoelectronic coupling elements or optocouplers, also called optoisolators or optoelectronic relays; serve, as are known, to provide feedback-free signal or one directional transmission between two electrically separated circuits, namely a primary and a secondary circuit. They generally comprise a luminescence or light emitting diode, namely a diode emitting light in the visible or infrared wavelength range (LED or IRED type respectively), and a detector, for example a photodiode or a phototransistor which are coupled optically. The advantages of optocouplers over mechanical relays are the elimination of any moving parts, their long life, small size, compatability with semiconductor circuits, and above all their high switching rate or fast response time.
In optocouplers, photoemitters and photoreceivers are usually mounted on separate lead frames and arranged so that as large a portion of the emission radiation as possible falls on the receiver surface of the photodetector. The optic coupling can be improved by an intermediate layer of synthetic material which brings about at the same time an increased amount of electric insulation.
In modern optocouplers, for the primary side and secondary side separate lead frames are utilized on which the transmitter and receiver chips are applied and contacted by the usual methods. The two tapes are brought together. The light channel is produced by dabbling, cladding or sealing. Thereafter the light channel is coated with a reflecting layer and the entire component is externally coated or clad with synthetic material to provide the finished product. Instead of two split lead frames, which permit constructing the transmitter and receiver chips opposite each other, a single lead frame method with coplanar construction of the transmitter and receiver chips may be used.
Due to the complexity of construction of an optoelectronic coupling element having, for example, an infrared transmitter chip, an insulating light transmission path (coupling medium) and a receiver chip such as arrangement is relatively costly.